LCD panels are widely used flat panel display devices. LCD panels are generally manufactured using microelectronic manufacturing techniques that are also used to manufacture integrated circuits.
In manufacturing LCD panels and integrated circuits, photolithography is generally used to pattern layers that are stacked on a substrate to form the LCD panel or integrated circuit. Masks are used to define the patterns. In order to produce high performance, high-quality devices, it is generally important that a succeeding mask layer is aligned to the pattern of a preceding mask layer. Alignment keys, also referred to as alignment marks, are often used to facilitate this alignment.
FIGS. 1A and 1B illustrate the use of alignment marks in integrated circuit manufacturing. As shown in FIG. 1A, an integrated circuit wafer 1 includes an array of spaced apart dies 2, which are the active regions that form integrated circuits. A scribing line 3 is used to divide the wafer into individual dies in the spaces between the dies. As shown in FIG. 1B, one or more alignment keys 4 are generally arranged in the space between dies. Although the alignment keys are indicated as being an "x", other shapes may be used. Subsequent masks are aligned to the wafer using the alignment keys 4.
A mask may be aligned to a wafer using the alignment keys 4 by first aligning the mask to a fiducial mark on a stepper. A midpoint or origin (0, 0) in the wafer is then found. This step is referred to as Wafer Global Alignment (WGA). A position of each exposure shot for the origin (0, 0) is obtained using the alignment keys 4 that are positioned in the space between the dies 2. The position of the alignment key for the origin point (0, 0) is set by the design. Errors between position values in the design and actual values obtained as described above, are checked. The wafer and the mask are then exposed after compensating for the error.
As shown in FIG. 1B, the alignment keys that are positioned in the spaces between integrated circuits are generally symmetrically arranged about a midpoint. Then, the positions of the alignment keys may be obtained by obtaining the positions of the alignment keys for the midpoint and averaging them.
As noted above, alignment keys are also used in manufacturing LCD panels. Conventional alignment in LCD panels will be described in connection with FIGS. 2A-2B and 3A-3B, which illustrate shot maps on the LCD panel. As used herein, a shot is defined as a region exposed on an LCD panel by a single radiation exposure. Reference number 5 indicates the alignment keys. It will be understood that although the alignment keys are shown in the form of an "x", different shapes of alignment keys may also be used.
FIGS. 2A and 2B illustrate shot maps when one mask per layer is used in manufacturing the LCD panel. The regions formed by dotted lines indicate shots exposed on the LCD panel in FIG. 2A. FIG. 2B illustrates a mask that may be used to form the LCD panel of FIG. 2A. As shown in FIGS. 2A and 2B, an A shot, a B shot and a C shot are repeatedly formed in the LCD panel of FIG. 2A, with the patterns for the A shot, the B shot and the C shot being formed in the mask of FIG. 2B. As shown, the A shot indicates an active region of an LCD panel, which is used as the display region.
Accordingly, the A shot on the LCD panel is aligned using the alignment keys inserted in the marginal areas of the B shot and C shot. Stated differently, the position for the A shot is obtained using the alignment keys in the B shot and the C shot. Unfortunately, this may degrade the alignment, since the position of the A shot is obtained indirectly using the alignment key in the B shot and in the C shot, rather than using an alignment key in the A shot.
FIGS. 3A and 3B illustrate shot maps when four masks per layer are used. FIG. 3A illustrates the shots exposed on the LCD panel and FIG. 3B illustrates the masks used when forming the LCD panel of FIG. 3A. As shown, the active region in the A shot may be aligned more accurately than in the LCD panel of FIG. 2, since the LCD panel may be aligned using an alignment key in the A shot. However, the region in which the alignment key can be inserted is generally limited to two sides. In particular, as shown in FIG. 3A, alignment keys may be placed in an upper side and left side of an A shot, in the upper side and right side of the B shot, in the lower side and left side of the C shot, and in the lower side and right side of the B shot. Accordingly, it may difficult to uniformly arrange alignment keys in the shots so that it may be difficult to obtain the high degree of alignment accuracy that may be conventionally obtained in manufacturing integrated circuit devices.
In summary, it may be more difficult to obtain accurate alignment in fabricating LCD panels. More specifically, it may be difficult to obtain accurate alignment between the gate lines, data lines and pixel electrodes. This may degrade the performance and/or reliability of the LCD panel.